Some areas may require you to break through walls to get around obstacles, but the action here is still pretty straightforward. In many areas, you can look into the next room by being close to a wall. This then allows you to use indirect fire powers (such as Storm's Blizzard) without fear of retaliation, especially if you can keep your party members from pathfinding their way through a door to attack your enemies.

You start to encounter several enemies with Invulnerability except to certain maneuvers.

You probably have to hit them several times with the indicated combo to deactivate the invulnerability.

Experiment with various characters to see if their powers will ignore this. For example, Scarlet Witch's Hex Bolt, Hex Locked, and Reality Shift can still damage targets even while their invulnerability is active.

Sugarman
Really tough in melee, and his tongue attack is quite fast. If you don't move quickly, he can hit you with it repeatedly and keep knocking you down.

He can hit you quickly and repeatedly with his Tongue attack and never give you a chance to act. If you can't get away from the Tongue attack, switch characters. He should then redirect his attention to another character as he is very focussed on pursuing whichever character you are controlling. Use the Call Allies function to have your party attack him instead of follow you.

The Tongue attack fires straight forward and cannot hit targets above, below, or to the side. You can therefore sidestep or jump away. You can also run and keep him frustrated by going up and down the stairs. This lets a support character cast group buffs or healing.

He needs to turn around to use his Tongue attack since it fires directly forward, so you could briefly switch characters to someone behind him and pound on him, then switch to another character once he has you targeted by his Tongue attack. A strong melee character can actually make short work of Sugarman in less than 30 seconds if you can stay on his flank.